In semiconductor manufacturing, functional integrated circuits can be fabricated on a semiconductor substrate by using a series of processes such as photolithography, etching, doping, deposition, planarizing, and cleaning. Among these processes, the photolithography process is especially important, because it may define areas for performing the etching and/or doping processes.
During the photolithography process, a photoresist layer is formed on a semiconductor substrate by a spin-on-coating technique and fixed or completely cured by a baking process first. Then, the formed photoresist layer may be put in a photolithography machine. Next, the photoresist layer may be exposed, transferring patterns in a mask into the exposed photoresist layer. Finally, the exposed photoresist layer may be baked and developed, forming patterns in the photoresist layer.
However, as the photoresist layer becomes thicker, the uniformity of the thickness may decrease significantly. Thus, the subsequent exposure process and other processes may be impacted. For example, the line width may change during the exposure process. Thus, the semiconductor manufacturing yields may decrease. Similarly, when forming other coating layers (e.g., polyimide) on the semiconductor substrate using the spin-on-coating technique, as the thickness of the coating layer increases, the thickness uniformity may decrease. The disclosed methods are directed to solve one or more problems set forth above and other problems.